 
ABERRATION - Any inherent deficiency of a lens or optical system which is
responsible for imperfections in shape or sharpness of the image.
ANGLE OF VIEW - May be expressed in Diagonal, Horizontal or, Vertical. Smaller
focal lengths give a wider angle of view
APERTURE - The opening of a lens that controls the amount of light reaching the
surface of the pickup device. The size of the aperture is controlled by the iris
adjustment. By increasing the F-stop number (F/1.4, F/1.8, F/2.8 etc.) less light is
permitted to pass to the pickup device.
APERTURE SCALE - The aperture scale is referred to as a F-number. The
international aperture scale is: F1, F1.4, F2, F2.8, F4, F4.6, F8, F11, F16, etc.
ASPHERICAL LENS - A lens which one or more of the elements have a non-spherical
surface. Aspherical surfaces are shaped to reduce the spherical and other
aberrations.
AUTOMATIC GAIN CONTROL (AGC) - A section in an electronic circuit that has
feedback and regulates a certain voltage level to fall within predetermined margins.
AUTO IRIS - An automatic method of varying the size of a lens aperture in response
to changes in scene illumination.
AUTO-IRIS LENS - A lens with a electronically controlled iris. This allows the lens to
maintain one light level throughout varying light conditions.
BACK FOCUS - Back focus is a term used to describe the relationship of the distance
of the lens to the image device. This distance is critical to maintain the proper depth
of field through changing focal lengths and varying light conditions. The correct back
focus is normally achieved by adjusting the image pick-up device on the camera
itself.
BACKLIGHT COMPENSATION - When filming in directions with backlighting such as
entrance-ways or windows where the backlighting causes the subject to appear as a
silhouette, this function automatically adjusts to the most appropriate aperture. Without
backlight compensation Subject appears as a silhouette against bright background.
BANDWIDTH - The amount of data that may be sent over a wire (commonly called a
network) is referred to as a band-width. At any one time this data is measured in
Kilobits, Megabits or Gigabits. As a short hand the first letter of each name is used.
An example would be that Kilobits is shortened to “K”. This measurement refers to
the number of “on and off signals” that can be sent per second. The average
household modem used to connect to the Internet operates at 28.8Kbps, which is
28,800,000 bits per second. Few, if any companies operate on a household modem
and we can apply this measure to the standard office network. The average network
operates at 10 Megabits, which is 10,000,000.00 (ten million) bits per second. That
is a big number and a lot of data traveling at one time. This number is generally
enough for 50 to a 100 average users or 10 to 15 people playing Real-Time Radio
over the Internet.
CHARGE-COUPLED DEVICE (CCD) - The new age imaging device, replacing the old
tubes. When first invented in the 1970's, it was initially intended to be used as a memory
device. Most often used in cameras, but also in telecom, fax machines, scanners, etc.
CLOSED CIRCUIT TELEVISION (CCTV) - Television system intended for only a
limited number of viewers, as opposed to broadcast TV. A CCTV Camera is a unit
containing an imaging device that produces a video signal in the basic bandwidth.
C-MOUNT - The first standard for CCTV lens screw mounting. It is defined with the
thread of 1"(2.54mm) in diameter and 32 threads/inch, and the back flange-to-CCD
distance of 17.526mm (0.69"). The C-mount description applies to both lenses and
cameras. C-mount lenses can be both, C-mount and CS-mount cameras, only in the later
case an adaptor is required.
CS-MOUNT - A newer standard for lens mounting. It uses the same physical thread as
the C-mount, but the back flange-to-CCD distance is reduced to 12.5mm in order to have
the lenses made smaller, more compact and less expensive. CS-mount
lenses can only be used on CS-mount cameras.
DC TYPE AUTO-IRIS - Auto-iris lenses where the iris is controlled by the circuitry of
the camera.
DEPTH OF FIELD - The regions in front of and behind the focused distance where the
image remains in focus. With a greater the depth of field, more of the scene near to far is
in focus. Lens aperture and scene lighting will greatly influence the D.O.F.
F-NUMBER - In lenses with adjustable iris, the maximum iris opening is expressed as a
ratioffocal length of the lens)/(maximum diameter of aperture). This maximum
iris will be engraved on the front ring of the lens. the brightness of the image formed by
the lens, controlled by the iris. The smaller the F-number the brighter the image.
F-STOP - A term used to indicate the speed of a lens. The smaller the F-number the
greater amount of light passes through the lens.
FIELD OF VIEW - The horizontal or vertical scene size at a given length from the
camera to the subject.
FOCAL LENGTH - The distance from the center of the lens to a plane at which point a
sharp image of an object viewed at an infinite position. The focal length determines the
size of the image and angle of FOV seen by the camera through the lens. This is the
center of the lens to the image pickup device.
GAIN - Any increase or decrease in strength of an electrical signal. Gain is measured in
terms of decibels or number times of magnification.
HUNTING - An industry term used to describe a auto-iris lenses inability to stabilize
under certain light conditions.
IRIS - A mechanical diaphragm which can be controlled manually or automatically to
adjust the lens aperture.
LENS FORMAT - The approximate size of a lens projected image. In most cases the lens
will project a image slightly greater than the designated image size to insure the pickup
device is completely covered. It is recommended that camera and lenses are the same
format size. A lens a larger format size can be used on a smaller format camera, however
a smaller format lens should never be used with a larger format camera.
LENS SPEED - Refers to the lens aperture or its ability to transmit light. This is
measured in F-stops.
LEVEL CONTROL - Used to set the auto-iris circuit to a video level desired by the user.
Turning the level potentiometer towards the HIGH position will open the iris allowing
more light to pass through the lens, towards the LOW will close the iris allowing less
light to pass through the lens.
MANUAL IRIS LENS - A lens with a manual adjustment to set the iris opening
(aperture) to a fixed position. This type lens is generally used in fixed lighting conditions.
MINIMUM OBJECT DISTANCE (M.O.D.) - The closest distance a given lens will be
able to focus upon a object. Generally the smaller the focal length the shorter the M.O.D.
This distance can be altered with use of extension tubes.
MINIMUM SUBJECT ILLUMINATION - This is minimum illumination required for
recognizing the subject. This is generally 2 to 6 lux for color cameras, and 0.1 tux for
black and white cameras. Also, minimum subject illumination changes according to the F
value of combined lenses. With F1.2 lenses and F1.4 lenses, combined with an F1.2 lens
minimum subject illumination is reduced, so that imaging is possible In dark locations.
PINHOLE LENS - A fixed focal length lens, for viewing through a very small aperture,
used in discrete surveillance situations. The lens normally has no focusing control but
offers a choice of iris functions.
PRE-POSITION LENSES - Pre-position lenses are specially designed lenses with extra
mechanical/electrical components to allow for computer interfacing. This function allows
the lens (when used with the appropriate controller) to feedback to the controller
information relevant to zoom and focus propositioning allowing the controller to quickly
scan to a pre-selected scene, arriving in focus at the proper zoom point without operator
intervention.
RESOLUTION - A measure of the ability of a camera or television system to reproduce
detail. The number of picture elements that can be reproduced with good definition.
SIGNAL-TO NOISE RATIO (S/N) - An S/N ratio can be given for the luminance signal,
chrominance signal and audio signal. The S/N ratio is the ratio of noise to actual total
signal, and it shows how much higher the signal level is than the level of noise. It is
expressed in decibels (dB). The bigger the value is, the crisper and clearer the picture and
sound will be during playback. An S/N ratio is calculated with the logarithm of
the normal signal and the noise RMS value.
SYNC - This is the timing used by the security camera when imaging (synchronizing).
There are sync systems that synchronize with the internal sync signal circuit
(internal sync.), or that synchronize with a sync signal input to the security
camera from outside (external sync.), or those that use the cycle of the
camera's AC power to synchronize (line lock). When switching between several
security cameras for surveillance using one monitor, synchronizing the cameras
is necessary. For this, the line lock and external sync systems are used.
WHITE-BALANCE (COLOR CAMERAS ONLY) light source changes, white
Sometimes, the color of clothes seen under lighting inside appears green when
viewed in sunlight outside. This is due to variation in the color temperature of
the light source. The human eye is highly adaptable to variation in the color
temperature of light sources so that even when the light source changes, white
appears as white. CCD adaptability is poor, and to reproduce unbalanced white
when the light source changes, correction of the image signal is necessary.
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